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Dynamic hydrogen isotope behavior and its helium irradiation effect in SiC Yasuhisa Oya and Satoru Tanaka The University of Tokyo

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Objective Structural materials for future fusion reactor SiC/SiC Composite Low activation Ferritic steel Vanadium alloy Thermal and chemical stability Understanding of hot atom behavior of hydrogen isotopes in fusion reactor circumstance Under high energy particles irradiation circumstance From the viewpoint of fusion safety Evaluation of Hydrogen isotope retention behavior and chemical states of SiC by D 2 + -He + irradiation by X-ray photoelectron spectroscopy (XPS) and thermal desorption spectroscopy (TDS)

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Experimental procedure Pretreatment D 2 + irradiation He + irradiation XPS (X-ray photoelectron spectroscopy) Annealing at 1300K for 10 minutes under the vacuum less than 10 -8 Pa Energy: 1.0 keV Flux : 1.3 x 10 18 D + m -2 s -1 Fluence : 1.0x10 22 D + m -2 Energy : 1.3 keV Flux : 1.3 x 10 18 D + m -2 s -1 Fluence : 0-1.0x10 22 D + m -2 TDS (Thermal desorption spectroscopy) X-ray source : Mg-KHeating rate : 0.5 K s -1 Temperature : 300-1300 K

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Sample and experimental system ROICERAM-HS Asahi Glass Co. Ltd. Polycrystalline -SiC(3C-SiC) : 10mm1mm density : 3.10 g/cm 3 SiC Sample The sample can be transferred between TDS chamber and XPS chamber without air exposure. XPS measurements were performed at room temperature. Base pressure 10 -8 Pa

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Comparison of TDS spectra from SiC with Si and graphite Thermal desorption spectra of D 2 from SiC (a) SiC (b) Si (c) Graphite Two D 2 desorption stages 1 st stage at 800 K2 nd stage at 1000 K (Deuterium bound to Si)(Deuterium bound to C)

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TDS spectra of D 2 from SiC as a function of D 2 + ion fluence D trapping states in SiC : Si-D, C-D Si-D C-D D is trapped by Si after saturation of C-D bonds. Si-D is a major chemical state in SiC. D/SiC=0.75 D 2 TDS spectra after D 2 + irradiation with various ion fluence D and He retention as a function of He + fluence D retention decreased by He + pre-irradiation. D retention was not changed by He + pre- irradiation above the fluence of 0.1 x 10 22 He + m -2.

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XPS spectra of Si and C from SiC as a function of heating temperature (a) C 1s(b) Si 2p By heating above 800 K, the peak position of C 1s was shifted to lower energy side, although that of Si 2p was almost remained in the lower energy side. Both peaks were recovered by heating about 1200 K. Summary of peak positions by heating

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TDS spectra of D 2 from SiC as a function of implantation temperature Comparison of deuterium retention in SiC and graphite By heating the sample at 573 K, the deuterium retention was decreased less than half. However, the deuterium retention was found even above 913 K. Implantation temperature dependence on deuterium retention in SiC

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D 2 and He TDS spectra as a function of He + post irradiation fluence D 2 desorption mainly consists of two stages. D trapped by Si decreased by He + post irradiation. Only D 2 + irradiation D 2 + -He + irradiation (1.010 22 He + m -2 ) He D2D2

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Chemical behavior of D 2 + irradiated SiC as a function of He + post irradiation fluence Si 2p C 1s By D 2 + irradiation, C 1s : High energy side Si 2p : Low energy side By He + irradiation, C 1s : Slight shift toward lower energy side Si 2p : Shift toward lower energy side Sensitivity of XPS C 1s : C-D bond and defects Si 2p : mainly defects D was trapped by SiC and some defects would be also introduced. By He + irradiation, more damaged structures were introduced.

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Isochronal heating for D 2 + -He + irradiated SiC (1) Si 2p C 1s By heating, C 1s was shifted toward low energy side and Si 2p was moved toward high energy side. After the dissociation of C-D bond, the damaged structures would be recovered. Above 1200K, both of C1s and Si2p were shifted to higher energy side. Peak positions of C 1s and Si 2p as a function of heating temperature

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Isochronal heating for D 2 + -He + irradiated SiC (2) * transition XPS spectra of C 1s after heating at 1300K By heating, D was detrapped and SiC structure would be recovered, which led to decrease FWHM. Above 1000K, C was aggregated on the surface and form C=C and/or C-C bonds, which contribute to increase FWHM.

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XPS spectra after heating at 1150 K and 1300 K 278282286290294 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 x 10 4 Binding Energy / eV c/s 278282286290294 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 x 10 4 Binding Energy /eV c/s Peak 1 Peak 2 Peak 1 Peak top: 284.23 eV, FWHM: 1.93 eV C-C bond Peak 2 Peak top: 282.98 eV, FWHM: 1.43 eV C-Si bond 1300 K1150 K Area ratio Peak1: Peak2 1150 K 45.4: 54.6 1300 K 75.0: 25.0 C was aggregated by heating at 1300 K.

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Depth profiling of C 1s and Si 2p after heating at 1300 K Chemical states of C and Si in SiC after heating 1300 K were evaluated by Ar + sputtering. C was aggregated on the surface. C 1s was largely shifted to lower energy side at the depth of a few nm. Decrease of C=C and/or C-C bond and only Si-C exists in the bulk of SiC Si-C bond is a major chemical state at the depth of 20nm(irradiation range . SiC structures were disordered by D 2 + and He + irradiation.

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Conclusions D 2 + irradiation was performed to SiC sample and thereafter, He + was irradiated to elucidate the correlation between behaviors of hydrogen isotope and the damaged structures. By He + irradiation to D 2 + irradiated SiC, deuterium retention decreased at the initial stage. D trapped by Si was desorbed, which indicates that the C vacancies interact with irradiated He +. It can be concluded that the knocked C produced by He + irradiation was aggregated by heating above 1300 K, which imply that the some C impurity would contaminate the plasma or the tritium breeding materials by contacting the SiC structural (insert) material.